Analytical methodologies were developed for the quantification of niobium, tantalum, iron and manganese in samples of minerals and solid residues coming from ore pressure leaching, using different acids. The adopted instrumental technique was X-ray fluorescence on pelleted solid samples. The analysis of the experimental data obtained by the different assayed methods showed that the direct technique using calibration curves built from pure oxide patterns and the method of standard addition were those giving statistically acceptable results. Comparison of the analytical data obtained by application to ore and leaching residue samples of these methods with a reference method showed that the experimental results were satisfactory.